So far there has been proposed, as an in-vehicle power supply device for lighting a headlight, a power supply device configured to be fixed under a lamp body in which a light source is housed (for example, see JP4727001B).
This type of power supply device includes: a printed circuit board on which a power supply circuit configured to convert an input power from an external power source into a suitable power to light a light source is mounted; and a casing which is made of metal and houses the printed circuit board. In a case where a high-intensity discharge lamp is employed as the light source, for example, the power supply circuit includes an inverter circuit configured to generate an AC power to keep lighting the light source.
The power supply device further includes: an input socket used for the connection to the power source; and an output socket used for the connection to the light source. Specifically, the input socket is configured to be connected to an input plug provided on a second end of an input cable of which first end is connected to the power source. Also, the output socket is configured to be connected to an output plug provided on a second end of an output cable of which first end is connected to the light source.
The printed circuit board is disposed so that a thickness direction thereof corresponds to the vertical direction. The casing is formed to be thin shape in the vertical direction. The output socket is fixed to an upper wall of the casing, and the input socket is fixed to a side face of the casing.
As seen from the vertical direction, the casing is smaller than the lamp body in the dimension, and thus the input socket fixed to the side face of the casing should be located under the lamp body. Therefore, in order to avoid interference between the input socket and the lamp body, the input socket is disposed so as not to further protrude upwards than an upper face of the casing (i.e., so as not to further protrude to the lamp body side than a face, facing the lamp body, of the casing).
Downsizing of the input socket is difficult due to need for securing the waterproof property. Therefore, the total size of the casing is agreed with the size of the input socket so that the whole of a bottom of the casing is positioned lower than a lower face of the input socket. This leads to increase the size of the casing.